In the United States, telephone service is provided by multiple providers or carriers. Some calls are handled by one service provider, e.g., a local call completed between two wired telephone stations. Other calls, e.g., long-distance calls, require multiple service providers to cooperate for their completion.
The initial carrier providing telephone service is a local service provider, illustratively a local exchange carrier (LEC), such as New Jersey Bell, but also including cellular (wireless), cable and any so-called "dial-tone provider" or "first contact service provider", all such being referred to herein as local service providers. The second carrier is typically, but not necessarily, a long-distance-or so-called inter exchange-telephone carrier. For example, presently, for a long-distance telephone call between wired telephone subscribers, the local service providers serving the calling and called telephones are LECs which are interconnected by a long-distance, or interexchange, carrier (IXC). In the United States, AT&T, MCI and Sprint are three such IXCs. In another example, for a local call from a mobile telephone to a wired telephone station, the local service provider is a cellular service provider while the second carrier could be a LEC that is connecting the network of the cellular service provider to a called party at the wired telephone station. Thus, it is possible for a telecommunications carrier to serve multiple roles, e.g., being the local service provider for some calls while being a second carrier for other calls.
Each telephone subscriber of a local service provider has associated with his telephone service a presubscribed default second carrier that was selected by or for the subscriber. The presubscribed default second carrier carries multiple-carrier calls originated from the subscriber's telephone unless the local service provider is instructed otherwise by way of the call-by-call entry of a telecommunications carrier code indicating which telecommunications carrier should carry the particular call. For any call for which a telecommunications carrier code is not entered, the default second carrier is typically identified based on the particular telephone link-illustratively represented herein by a wired telephone line but also including wireless (cellular), fiber optic or cable connections and any other link provided to connect telephones to local service providers-on which the local. service provider received the call.
Continuing with the above-described interexchange call example, which represents the most common scenario at present, each subscriber to local telephone service from a LEC has associated with his telephone line a "primary interexchange carrier," or PIC. The local subscriber is said to be "PIC'd" to the associated IXC. The interexchange carrier to which a subscriber is PIC'd will be used by default to complete interexchange calls originated from his telephone line unless the LEC is instructed otherwise. Such instruction is given when the subscriber enters, on a call-by-call basis, prior to dialing the called telephone number, a telecommunications carrier code, illustratively an IXC access code, corresponding to the desired IXC. One such IXC access code is "10 2 8 8" (10 A T T) corresponding to AT&T.
Specifically, when a long-distance call is initiated by the subscriber from his telephone line, and no access code is entered prior to the dialing of the called telephone number, the call is routed through the network of the originating subscriber's LEC, over the network of the PIC'd IXC and, ultimately, through the network of the LEC which has as one of its subscribers the terminating subscriber. Alternatively, a subscriber may initiate a long-distance call by dialing, prior to supplying the called telephone number, an IXC access code that indicates which of the IXCs he wishes to carry his call. Upon receipt of the access code by a switch of the LEC serving the caller, it is recognized that the caller wishes his call to be carded over the IXC corresponding to the received access code. Accordingly, the LEC routes the caller's call to a trunk connecting the LEC to the IXC indicated by the access code, regardless of the IXC to which the caller's telephone line is PIC'd. Thereafter, the LEG passes the called telephone number to the selected IXC. It is noted that the supplying of an IXC access code typically indicates the selection by the caller of an IXC other than the one that he is PIC'd to, but occasionally it may indicate the same IXC to which the caller is PIC'd.